1. Technical Field
The present invention relates to liquid ejecting heads provided in liquid ejecting apparatuses such as ink jet printers and to liquid ejecting apparatuses provided therewith, and particularly relates to liquid ejecting heads and liquid ejecting apparatuses capable of suppressing unnecessary vibrations occurring when ejecting a liquid.
2. Related Art
A liquid ejecting apparatus is an apparatus that includes an ejecting head, and that ejects various types of liquid from this ejecting head. Image recording apparatuses such as ink jet printers, ink jet plotters, and so on can be given as examples of such a liquid ejecting apparatus, but recently, such technology is also being applied in various types of manufacturing apparatuses that exploit an advantage in which extremely small amounts of liquid can be caused to land in predetermined positions in a precise manner. For example, such technology is being applied in display manufacturing apparatuses that manufacture color filters for liquid-crystal displays and so on, electrode formation apparatuses that form electrodes for organic EL (electroluminescence) displays, FEDs (front emission displays), and so on, chip manufacturing apparatuses that manufacture biochips (biochemical devices), and the like. While a recording head in an image recording apparatus ejects ink in liquid form, a coloring material ejecting head in a display manufacturing apparatus ejects R (red), G (green), and B (blue) coloring material solutions. Likewise, an electrode material ejecting head in an electrode formation apparatus ejects an electrode material in liquid form, and a bioorganic matter ejecting head in a chip manufacturing apparatus ejects a bioorganic matter solution.
With this type of liquid ejecting apparatus, there is a strong demand to increase the speed of the liquid ejection. Accordingly, there is demand for pressure generation units (for example, piezoelectric vibrators, thermal elements, and so on) provided in the liquid ejecting head to operate at higher speeds. However, in the case where the driving frequency (the ejection frequency of the liquid) is increased beyond the driving frequencies used in the past, the amount of the liquid ejected through the nozzles in the liquid ejecting head or the flight speed thereof (for simplicity's sake, these will be referred to as the “ejection properties” hereinafter) fluctuates in accordance with the driving frequency. It is thought that this is caused by the state of the meniscuses in the nozzles. In other words, if the time between a given liquid ejection and the subsequent liquid ejection is reduced, the subsequent ejection will be carried out before vibrations in the liquid within pressure chambers including the nozzles (and in particular, in the meniscuses) immediately after the previous ejection have sufficiently converged, and such differences in the meniscus states will result in fluctuations in the ejection properties. Accordingly, it is desirable to suppress vibrations in the meniscus caused by the ejection of the liquid to the greatest extent possible.
With respect to this point, JP-A-2005-119296 discloses a design for a liquid ejecting head structure that fulfills c2/V<16π2μ2l0/(A3ρ2), where the V represents the volume of a pressure chamber, A represents the cross-sectional area of a nozzle, l0 represents the length of the nozzle in the axial direction, ρ represents the density of the liquid, μ represents a viscosity coefficient for the liquid, and c represents the transmission speed of pressure waves that traverse the liquid within the pressure chamber. Through this, the meniscus in the nozzle does not vibrate, and when a driving waveform is applied, unique vibrations in the meniscus do not pose a problem, and there are no time restrictions and cycle restrictions; accordingly, efficient driving can be carried out, without needing to take into consideration the time for applying the driving waveform.
Generally speaking, in this type of liquid ejecting head, a liquid chamber that is common among the plurality of pressure chambers (also called a “reservoir” or “manifold”) is provided, and this common liquid chamber and the pressure chambers communicate via supply channels (supply openings). The supply channels are flow channels whose cross-sectional areas are set to be sufficiently smaller than those of the reservoir, the pressure chambers, and so on, and are provided in order to adjust the flow channel resistance, the inertance, and so on with respect to the nozzles. In other words, the supply channels are important elements that are significantly related to the properties of the ejection of the liquid from the nozzles, and are designed with a balance between the flow channel resistance and the inertance of the nozzles in mind.
However, with the invention disclosed in the aforementioned JP-A-2005-119296, no attention is given to the supply channels, and there is the possibility, in the case where a liquid is ejected through the nozzles at a higher driving frequency, that the desired ejection properties cannot be obtained due to an insufficient supply of liquid from the common liquid chamber to the pressure chambers through the supply channels, and so on. Accordingly, for the purposes of practical use, it is desirable to implement a design that also takes into consideration the aforementioned property of the supply channels.
It should be noted that these problems are not limited to ink jet recording apparatuses, and are also present in other liquid ejecting apparatuses that eject liquids aside from ink.